Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are typically inserted through an insertion opening of an ink loader for the printer, and the ink sticks are pushed or slid along the feed channel by a feed mechanism and/or gravity toward a heater plate in the heater assembly. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to an ink reservoir which maintains the ink in melted form for delivery to a print head for jetting onto a recording medium.
One difficulty faced during operation of solid ink printers is the ink reservoirs exhausting the available supply of melted ink and running dry. If a reservoir were to run dry, the printing system may suffer a catastrophic failure and be unable to print. When the ink level in an ink reservoir reaches or falls below a “low” ink level, a melt duty cycle is initiated in order to refill the reservoir with melted ink. However, if a melt duty cycle is initiated and there are no ink sticks engaging the melt plate, the continued generation of heat by the melt plates may damage the heater and adjacent components because an ink stick helps absorb heat generated by the melt plate and aids in temperature regulation of the melt plate.
Ink sticks may not be available to engage the melt plate during a melt cycle. Unavailability of ink sticks may arise from ink out or ink jam conditions. An ink out condition occurs because a feed channel has exhausted its available supply of solid ink sticks. An ink stick jam condition arises when one or more ink sticks have gotten trapped or jammed in an ink feed channel prior to reaching the melt plate at the end of the channel. Ink stick jams may occur due to ink sticks becoming skewed in the respective feed channel as they are being fed toward the melt plate and/or due to ink stick particles and debris accumulating in a feed channel and blocking or interfering with ink stick travel in the feed channel.
The absence of an ink stick at a melt plate in a feed channel may be detected by monitoring the temperature of the melt plate using the melt plate temperature sensor, e.g., thermistors, and comparing the sensed temperature to a predetermined temperature indicative of no ink stick being present at a melt plate. In response, the controller interrupts the application of power to the melt plate, printing is disabled, and a user intervention fault is declared. For example, a user intervention fault may include alerting the printing operator to the ink out or ink jam condition. The operator may also be prompted to take corrective action such as inserting ink sticks into the feed channel corresponding to the overheated melt plate or attempting manual removal of jammed ink sticks from the feed channel.